In the operation of electrophotographic or laser printers, it is a standard procedure to use a so-called "beam detect" signal derived from a laser print engine to control the timing or start at which each successive line of video input data is applied to the laser print engine. This beam detect signal is derived from a photodetector which is located and focused with respect to the edge of the photoconductive drum across which the laser beam is swept so as to detect the start of each successive video line scanned. The beam detect signal is picked up by the photodetector and then synchronized to an asynchronous clock signal which is used to set the modulation frequency for the video data being applied to the laser engine.
The problem with using the above approach is that since the beam detect signal is synchronized to an asynchronous clock, the phase of the asynchronous clock signal is not necessarily the same phase as the beam detect signal, and this fact, in turn, produces a phenomenon in the printed image which is known in the art as "jitter". This jitter is produced by not precisely spacing dots on each successive printed line with respect to the dots spaced on each previously printed and successively printed line. It is the solution to this problem to which the present invention is directed.